Update documentation for Python interface (#1208)
Update documentation for Python interface (#1208)

* Add PySB import, PEtab import, plain ODEs (Closes #654)
* Cleanup
* Update
AMICI-developer/AMICI,FFroehlich/AMICI,FFroehlich/AMICI,AMICI-developer/AMICI,FFroehlich/AMICI,AMICI-developer/AMICI,AMICI-developer/AMICI,FFroehlich/AMICI